Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Pretty diffraction patterns

  1. Dec 17, 2008 #1
    I was wondering whether anyone could suggest ways of making nice diffraction patterns using a red laser. I work at a charitable school in Kazakhstan so am limited in terms of materials. Any suggestions would be appreciated. Thanks
  2. jcsd
  3. Dec 18, 2008 #2
    What kind of diffraction patterns do you want to look at?

    Do you have an old CD or DVD laying around? Bouncing a laser off of that, it acts as a diffraction grating.

    You can use two razor blades mounted to make a nice single slit. You can even put a thin wire between them on one end, and make the blade edges touch at the other, and have a continuous variable width single slit.

    I've seen double slits made with two razor blades and a thin wire.
  4. Dec 18, 2008 #3
    Turn the lights off in the lounge or kitchen etc .. and fire the laser beam at all sorts of stuff ..

    Personally i like aiming at frosted or florescent light bulbs , but you will find all sorts of objects that work well in this regard (especially glancing angles where you aim at the edge of an object .
  5. Dec 18, 2008 #4
    Two more ideas. One that was done at my university and the photos featured in the Serway undergrad text...if you have a beam expander, make the beam larger than whatever small coin you have there. We generally use a penny or a dime, which are 9.25mm and 8mm in diameter, and are suspended by the thinnest thread we can find. When projected in a dark room, with a good expanded beam, you can see the shadow of the coin within the beam on a target some distance away. You will also see a bright spot in the CENTER of the target--a bright spot that can only be there because of diffraction. If it isn't clear, try moving the target closer or farther away--I don't recall the exact distance we used, but it was within an indoor laboratory.

    Also, try stretching a hair straight and shining the laser on it. Try different hairs--see if the students can rank the hairs by thickness based on the diffraction pattern.

    Use a piece of foil--even a candy wrapper--and make a tiny pinhole in it. I have made really small ones by placing the foil on a piece of glass, and tapping the pin on the surface of the foil. You'll see a circular aperture diffraction pattern--bright center spot, alternating dark/light rings.
  6. Dec 18, 2008 #5
    I found another I remembered--do you have a decent laser printer and transparency sheets that will work in it?

  7. Dec 18, 2008 #6
    I love this site! Thank you so much for all these great ideas. I will try experimenting. The laser jet prints look amazing but I don't think we have the laser jet :-(

    P.S. if we were investigating hair width based on the diffraction pattern is there an equation we would need?

    Thanks again!
  8. Dec 18, 2008 #7
    I would investigate first without an equation if i was you p.t .
    Bring forth equation from observation is a encouraging cycle .

    Another thing to mention is that by reflecting the coherent bean obliquely off an object you can achieve a primary dispersion pattern ..

    The secondary linear filtering of this pattern through a window can reduce the Photon beam considerably .. which can be interesting .

    Also using some small electric fans as oscillating gates the beam can be further reduced in volume ..

  9. Dec 18, 2008 #8
    You could "calibrate" the hair-measuring laser setup by using wire of known thickness...maybe magnet wire. Measure the characteristics of the diffraction pattern with the various thicknesses of wire, look for a mathematical relationship between the pattern and the wire thickness, then interpolate or extrapolate to the thickness of the hair.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?